The purpose of this study is to: 1) Determine if the measurement of FAS secretion induced by GnRH pulsatile administration distinguishes GnRH deficiency from constitutional delay of puberty. 2) Examine the GnRH regulation of FAS in patients with constitutional delay of puberty. 3) Examine the GnRH-induced response of FAS during the earliest phases of GnRH replacement in patients with GnRH deficiency.